1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a technique which is effectively applicable to a liquid crystal display device having high resolution such as a liquid crystal television receiver set.
2. Description of the Related Art
Conventionally, an active-matrix-type liquid crystal display device has been used in a liquid crystal television receiver set and the like, for example. The active-matrix-type liquid crystal display device includes a liquid crystal display panel which seals a liquid crystal material between a pair of substrates, and switching elements (also referred to as active elements) such as TFTs are arranged in a matrix array on one substrate out of the pair of substrates.
The conventional liquid crystal display panel has, for example, the circuit constitution shown in FIG. 7 in general. FIG. 7 is a schematic circuit diagram showing one example of the circuit constitution of the conventional liquid crystal display panel. FIG. 7 shows the constitution in which four pixels are arranged in an x direction.
In the conventional liquid crystal display panel, for example, on one substrate out of the pair of substrates (hereinafter, referred to as TFT substrates), a plurality of scanning signal line GL (GL1, GL2, . . . ) which extends in the x direction in an elongated manner, and a plurality of video signal lines DL (DL1, DL2, DL3, DL4, DL5 . . . ) which extends in the y direction in an elongated manner are formed, and pixels each of which includes a TFT and a pixel electrode PX are arranged in a matrix array in the x direction as well as in the y direction. Here, a gate of the TFT is connected to the scanning signal line GL, a drain of the TFT is connected to the video signal line DL, and a source of the TFT is connected to the pixel electrode PX. Further, the pixel electrode PX forms a pixel capacitance (also referred to as a liquid crystal capacitance) together with a liquid crystal material LC and a common electrode CT.
Further, in the liquid crystal display panel which corresponds to a color display used in a liquid crystal television receiver set or the like, four pixels shown in FIG. 7 are referred to as subpixels. When an RGB-method color liquid crystal display panel is adopted as the liquid crystal display panel, one dot of an image is constituted of three sub pixels, that is, a sub pixel which performs a display of R (red), a sub pixel which performs a display of G (green), and a sub pixel which performs a display of B (blue). Here, the plurality of pixels (sub pixels) which is arranged in the x direction is periodically arranged in order of the sub pixel which performs the display of R (red), the sub pixel which performs the display of G (green) and the sub pixel which performs the display of B (blue), for example.
Further, in the conventional general liquid crystal display panel, one scanning signal line GL is arranged for the plurality of pixels arranged in a row in the x direction, and TFT elements of the plurality of pixels which are arranged in a row in the x direction are connected to a common scanning signal line GL (GL1). In the same manner, one video signal line DL is arranged for the plurality of pixels arranged in a row in the y direction, and TFT elements of the plurality of pixels arranged in a row in the y direction are connected to a common video signal line DL.
However, in case of the liquid crystal display panel having the pixel constitution shown in FIG. 7, for example, the number of drive circuits (data drivers) which generate video signals (gradation voltages) which are inputted to the respective video signal lines DL is increased thus giving rise to drawbacks that the power consumption is increased, and a potential of the video signal becomes unstable along with the increase of heat value of the data driver thus lowering image quality, for example.
Accordingly, in a recent liquid crystal display panel, for example, as shown in FIG. 8, there has been proposed a liquid crystal display panel having the circuit constitution referred to as a double-scanning line method in which, with respect to the plurality of pixels arranged in a row in the extending direction of the scanning signal lines GL, one video signal line DL (DL1, DL2, . . . ) is arranged for every two neighboring pixels, and two scanning signal lines GL ( . . . , GLn−1, GLn, GLn+1, GLn+2, . . . ) are arranged to sandwich the plurality of pixels arranged in a row. FIG. 8 is a schematic circuit diagram showing one example of the circuit constitution of a conventional liquid crystal display panel which adopts a double-scanning line method. FIG. 8 shows the constitution in which four pixels are arranged in an x direction.
Here, the plurality of pixels arranged in the x direction is configured such that the pixel which has a gate of a TFT thereof connected to the scanning signal line GLn+1 and the pixel which has a gate of the TFT thereof connected to the scanning signal line GLn are alternately arranged. One example of a display method of an image in the liquid crystal display panel having such circuit constitution is briefly explained in conjunction with FIG. 9A and FIG. 9B. FIG. 9A is a schematic circuit diagram showing one constitutional example of the conventional liquid crystal display panel which adopts the double-scanning line method and polarities of pixel electrodes within 1 frame period. FIG. 9B is a schematic view showing one example of a driving method of the liquid crystal display panel having the constitution shown in FIG. 9A.
In the liquid crystal display panel having the double-scanning line method circuit constitution shown in FIG. 8, assume a row which is constituted of the plurality of pixels arranged in the x direction as a pixel row, for example, as shown in FIG. 9A, the relative positional relationship (connection relationship) among the TFT of each pixel, the scanning signal line GL and the video signal line DL agrees with each other in all pixel rows. In displaying video data amounting to 1 frame period on the display panel having such constitution, for example, as shown in FIG. 9B, a common voltage Vcom applied to common electrodes CT is set to a fixed value, and the respective scanning signal lines GL ( . . . , GLn, GLn+1, GLn+2, GLn+3, GLn+4, GLn+5, GLn+6, . . . ) sequentially turn on the scanning signal at fixed time intervals. Here, to the video signal line DL1, for example, as shown in FIG. 9B, a video signal (gradation voltage of positive polarity) having a potential of equal to or higher than the common voltage Vcom is inputted in conformity with timing that the scanning signal of the scanning signal line GLn is turned on, while a video signal (gradation voltage of negative polarity) having a potential of equal to the common voltage Vcom or lower than the common voltage Vcom is inputted, in conformity with the timing that the scanning signal of the scanning signal line GLn+1 is turned on. Thereafter, each time the scanning signal line on which the scanning signal is turned on is changed, the gradation voltage of positive polarity and the gradation voltage of negative polarity are inputted alternately.
However, when the video signal and the scanning signal are inputted by the method shown in FIG. 9B, the polarities of the respective pixels when the video data amounting to 1 frame period is displayed become a polarity as shown in FIG. 9A, for example. Here, in FIG. 9A, “+” indicated in respective pixel electrodes PX implies that the gradation voltage of positive polarity is written in the pixel electrode PX, while “−” indicated in respective pixel electrodes PX implies that the gradation voltage of negative polarity is written in the pixel electrode PX. That is, in case of the liquid crystal display device having the constitution shown in FIG. 9A and FIG. 9B, the pixel electrodes of the plurality of pixels arranged in the extending direction of the video signal lines DL assume the gradation voltages of the same polarity. Accordingly, for example, there may be a case that stripes in the longitudinal direction appear on a display screen thus lowering display quality.
Further, with respect to the above-mentioned liquid crystal display panel which adopts the double-scanning line method, for example, as disclosed in patent document 1, there has been known a liquid crystal display panel having the circuit constitution which prevents the occurrence of a phenomenon referred to as line crawling so as to enhance display grade (display quality). The circuit constitution described in patent document 1 may be configured as shown in FIG. 10, for example, wherein a liquid crystal drive voltage which inverts the polarities of pixel electrodes for every pixel of multiplication of 2 in the direction along the video signal line DL and, at the same time, inverts the polarities of the pixel electrodes for every 2 pixels controlled by the same data line in the direction along the scanning signal line GL is added to respective pixel electrodes. Here, FIG. 10 is a schematic circuit diagram showing the arrangement of TFTs and the polarities of respective pixel electrodes by reference to the circuit constitution described in the following patent document 1.    [Patent document 1] JP-A-11-326869 (corresponding U.S. Pat. No. 6,552,707)
However, in the conventional liquid crystal display panel which adopts the double-scanning line method, in general, the common voltage Vcom applied to the common electrodes CT is fixed and hence, the data driver is required to form the video signal (gradation voltage) which adopts amplitude twice as large as potential difference between the common voltage Vcom and the maximum gradation voltage of positive polarity as maximum amplitude. Accordingly, in case of the liquid crystal display device of high resolution such as a liquid crystal television receiver set, even when the double-scanning line method is adopted, there exists a drawback that a heat value of a data driver is high, and a potential of the video signal becomes unstable and hence, image quality is liable to be easily lowered.
Further, in driving the liquid crystal display panel, for example, it is desirable to adopt dot inversion driving which can realize a high-quality display with high contrast and low crosstalk. That is, it is desirable that the polarities of the gradation voltages written in the pixel electrodes of two neighboring pixels in the extending direction of the scanning signal line and the polarities of gradation voltages written in the pixel electrodes of two neighboring pixels in the extending direction of the video signal line always become polarities opposite to each other.
However, for example, to make the liquid crystal display panel having the constitution shown in FIG. 9A perform the dot inversion driving, it is necessary to invert the order of positive polarity and negative polarity of the video signal applied to one video signal line DL (for example, DL1) for every two pixels in order of positive polarity, negative polarity, negative polarity, positive polarity, positive polarity, negative polarity, . . . and, at the same time, it is necessary to invert the polarity of the video signal applied to two neighboring video signal lines (for example, DL1 and DL2). Accordingly, the number of times for inverting the polarity is increased thus giving rise to a drawback that the potential of the video signal is liable to easily become unstable.
Further, for example, in case of the liquid crystal display panel having the constitution shown in patent document 1 (FIG. 10), display quality is enhanced using a driving method different from dot inversion driving. This gives rise to a drawback that dot inversion driving is difficult.